Functional characteristics of intraepithelial lymphocytes from mouse small intestine. II. In vivo and in vitro responses of intraepithelial lymphocytes to mitogenic and allogeneic stimuli.

Although isolated intraepithelial lymphocytes (IEL) have been shown to have specific and non-specific cytolytic functions, their ability to proliferate in response to T-cell mitogens or alloantigens is controversial. Here we show that IEL from mouse small intestine do not respond to mitogens such as concanavalin A and phytohaemagglutinin A or in mixed lymphocyte reactions unless an accessory spleen cell is also present. Adherent spleen cells possess the most potent helper function, but a dividing accessory cell may also be required. Supernatants from stimulated lymphocytes also assist IEL to proliferate in vitro, particularly in the presence of adherent accessory cells. IEL could not mediate lethal graft-versus-host disease in irradiated hosts, but could produce popliteal lymph node hypertrophy or splenomegaly in unirradiated hosts. Thus, IEL have the potential for proliferative activities characteristic of T cells, but they require accessory cells and/or factors such as interleukin-2 for their function in vitro and in vivo.